1. Field of the Invention
The present invention relates to a semiconductor device, especially having a logic circuit and a delay circuit.
2. Description of the Related Art
Inside of a semiconductor circuit, desired functions can be achieved by successive operations that are a logical operation process in a logic circuit for several signals, and after that, a timing adjustment in a delay circuit and an output of signals to a next processing portion. Hereby, the logic circuit frequently gives priority to one of the requests described below.
Fast operation
Low electric current consumption
A space saving
In addition, the logic circuit is largely influenced by dispersions of processing time caused by the dispersions described below.
An element parameter dispersion
A power-supply voltage dispersion
A temperature dispersion
Especially in recent years, operation voltage becomes low voltage and comes to be used in a region near a threshold voltage of a transistor, so dispersions tends to be larger than before.
On the contrary, the delay circuit is designed to give priority to the request of the following (4) than the requests of the following (1) to (3), so dispersions depending on each condition are smaller than the logic circuit which performs the logical operation process of signals.    (1) Fast operation    (2) Low electric current consumption    (3) A space saving    (4) An accuracy of time measurement
Functions as a semiconductor circuit are achieved by the combination of the logical operation process of the logic circuit and the delaying operation of the delay circuit. However, dispersions of the processing time when these circuits are connected in series are averaged by the percentage of time which is occupied by these circuits during the operation period. So, the dispersions become large compared to the case when every circuit are composed of only the delay circuits. This becomes more pronounced when the processing time for one logical operation process becomes large by the low voltage.
Besides, in a process which combines plural signals, if an arriving order of each signal is reversed, it may cause a malfunction. The reverse of the arriving order of signals is easy to occur when the effect of various dispersions become large, because the percentage of the logical operation time and the delaying time are different in each path.
A synchronous semiconductor memory device to improve dispersion of timing is described in the patent document Japanese Patent Application Laid-open No. 2003-168292.